Previous compositional and immunological studies have defined the chemical and antigenic structure of the group-specific carbohydrates for Groups A, A variant and C streptococci. These polysaccharides were shown to have a common core structure. Work is in progress to determine the structure of the group specific carbohydrate of the Group B streptococcus in order to chemically define its antigenic determinants and to determine its chemical relationship to the other streptococcal group specific carbohydrates.